The Marussia team's decision to release Timo Glock from his contract for "commercial" reasons has focused attention on an aspect of Formula 1 that some see as unsavoury and more casual viewers probably did not even realise existed.

The truth is that "pay drivers" - those who bring sponsorship with them to secure a seat - have been a fact of life for as long as the sport has existed.

For teams such as Marussia, who started life back in 2010 as Virgin, the need for a driver to bring money in order to help the team reach their annual £40m budget is just something they have to accept.

Marussia, in fact, have done more than that. They were admirably open in their press release announcing Glock's departure that pay drivers were part of their business model.

Fangio's state funding

One of the sport's greatest, Argentine Juan Manuel Fangio, was a five-time world champion in the 1950s, but he would probably never have made it to Europe without the backing of Juan Peron's government.

What their news release said was that previously they felt they could manage with one pay driver and one salaried, with external sponsorship making up the budget.

That one pay driver this year was initially planned to be Englishman Max Chilton. However promising Chilton is, there is no secret that part of the reason he is there is his financial backing.

But now, Marussia said, the global economic downturn had changed things. External sponsorship was proving harder to come by and that meant they could no longer afford Glock's salary.

Glock introduced sponsors to the team, but his salary was significantly greater than what they paid. Chilton owes his drive to the fact that his 'salary' is far less than the income from the sponsors he brings with him.

There has been an outpouring of sympathy for Glock's predicament from his colleagues.

McLaren's Jenson Button, a world champion, and Red Bull's Mark Webber, a multiple race winner, were among those who sent messages of condolence and best wishes to Glock on the social networking site Twitter.

Glock might not be in the same league as leading names such as Fernando Alonso, Lewis Hamilton and Sebastian Vettel, but he was good enough to finish on the podium three times, among other strong performances, in his two years with the Toyota team in 2008-9.

It was Toyota's decision to quit F1 abruptly at the end of Glock's second season with the team that meant he ended up at Virgin/Marussia. Without a drive and with no competitive seats available, he took a chance that they would quickly make progress.

Heikki Kovalainen was in a similar situation at the end of 2009 after being dropped by McLaren. He ended up at Lotus Racing, another new team, who are now called Caterham.

Now the Finn, who won a race in 2008, is also set to drop out of F1. His Caterham team will take a second pay driver alongside Frenchman Charles Pic for this season.

Diniz's family value

Brazilian Pedro Diniz drove for Forti, Ligier, Arrows and Sauber during a career financed by his father's supermarket chain and other business interests. Despite achieving some modest points finishes, he's best remembered for escaping a huge fire during the 1996 Argentine GP (above).

It's not hard to see the appeal of pay drivers. Last year, Kovalainen was earning in the region $2.5m, while team-mate Vitaly Petrov brought about $10m in sponsorship.

Petrov not only finished ahead of Kovalainen in the championship but, by finishing ahead of Pic, then at Marussia, in the final race of the season. the Russian secured his team 10th place in the constructors' championship, which was worth $11m.

To put those numbers into context, the highest earner in F1 this season will be Hamilton on $31m (£19.6m), some way ahead of Alonso on a reputed 15m euros (£12.7m).

Money influences decisions up and down the grid and what constitutes a 'pay driver' is not black and white.

Sergio Perez, Button's team-mate at McLaren this year, owed his arrival in F1 with Sauber in 2011 to significant financial backing from his home country Mexico. In that sense, he was a pay driver.

Now, insiders expect McLaren's Mexican sponsorship portfolio to grow as a result of his joining the team. So was the lure of potential sponsorship one of the main reasons McLaren took Perez and is he still therefore a 'pay driver'?

Team boss Martin Whitmarsh says not, but there was surprise up and down the pit lane that McLaren did not instead choose German Nico Hulkenberg, whose performances have arguably been more impressive, but who is not linked to significant funding. Hulkenberg, ironically, is now at Sauber, where novice Esteban Gutierrez owes his presence to those Mexican backers.

Meanwhile, Perez's former Sauber team-mate Kamui Kobayashi, who has looked every bit as good in the last two seasons, is without a drive because he doesn't have sufficient sponsorship backing.

Then there is Williams. They signed Venezuelan Pastor Maldonado at the start of 2011 because of £30m-a-year in sponsorship money from his home country's national oil supplier, a deal that was approved personally by the President Hugo Chavez.

No-one is saying Perez and Maldonado don't deserve to be in F1. They clearly do. Maldonado, while wild, has already won a race, superbly, in Spain last year, holding off Alonso no less. And Perez will presumably win races for McLaren.

Media playback is not supported on this device

F1's greatest drivers - Number 2: Juan Manuel Fangio

In their case, their budgets smoothed their path to a job they deserve on ability anyway. With some lower down the grid, that is less clear.

This is just the way of the world in an expensive sport. And depending on how you look at it, even the careers of the very greatest are influenced by money.

Argentine Juan Manuel Fangio, a five-time world champion in the 1950s, would probably never have made it to Europe without the backing of the government of Juan Peron.

Vettel would not be in F1 without Red Bull funding him pretty much from childhood. Likewise, Hamilton's career had until this year been almost completely financed by McLaren. Ferrari would have signed Alonso anyway, but the fact he was going there certainly smoothed the path to them getting a big sponsorship deal with Spanish bank Santander, and vice versa.

The fact is, every driver on the grid has had to find funding to make their way through the ranks to F1.

The bigger concern for F1 right now is that this situation is becoming more and more prevalent - and Glock's predicament is the perfect illustration.

External sponsorship money is harder and harder to come by. In the financial crisis, the money is simply not there.

For some time now, it has been clear that F1 teams were finding it increasingly difficult to make ends meet. Businesses struggle when they either don't have enough income or their costs are too high. In F1, in the current global climate and with budget restriction not working as well as some would like, both apply.

That raises difficult questions for the teams and for the sport itself.

Ferrari will always be there. Red Bull are secure as long as owner Dietrich Mateschitz feels it suits his purposes; likewise Mercedes and their corporate board.

Even McLaren are affected. Now forced to pay for their Mercedes engines for the first time, they have seen Hamilton leave, partly because they could or would not get close to matching the salary Mercedes were offering him.

External sponsorship money is harder and harder to come by. In the financial crisis, the money is simply not there

Below that, every team has concerns about funding, to a greater or lesser extent, and there is a constant threat that one or more of them might not survive - as HRT did not last season.

That brings into question the whole F1 business model. If there is not enough external sponsorship out there to maintain the whole grid, where will the money come from to keep the sport's wheels turning?

Currently, teams get their funding from sponsors and from TV companies, who do their deals with F1 boss Bernie Ecclestone, who then distributes about half the funds to the teams. But TV companies, with one or two exceptions, are also feeling the pinch.

Meanwhile, one alarming statistic is regularly trotted out. F1's entire global TV rights income is about the same as that of the Turkish football Premier League - in the region of $490m.

Most are astonished to hear that, but it seems as if it's accurate, as far as these figures can be accurately assessed. Which raises questions about whether the sport is being marketed and promoted as effectively as it might be.

Teams under threat; questions about their financial models for all but the very richest; and also about whether the sport is making the most of its huge global appeal.